This invention relates to an improved method of moisturizing shirred cellulose casing, normally referred to as skinless sausage casing.
Tubular cellulosic casing is well-known, and has been widely used for many years by numerous manufacturers. The basic process for manufacturing regenerated cellulosic casings is through the well-known viscose process, which creates a liquified colloidal dispersion of cellulose fibers in an alkaline liquid carrier. Viscose is described in English Patent 8700 to Cross, Bevan and Beadle. Patents such as U.S. Pat. No. 1,036,282 to Lilienfield refine the compositions. U.S. Pat. No. 1,070,776; U.S. Pat. No. 1,158,400; U.S. Pat. No. 1,163,740 to Cohoe and Fox describe use of viscose to manufacture a tubular cellulosic casing. Henderson, U.S. Pat. No. 1,601,686; U.S. Pat. No. 1,612,508; U.S. Pat. No. 1,645,050; U.S. Pat. No. 1,654,253 provide basic technology to manufacture viscose into tubular casings with regenerating baths touching the inner and outer surfaces of the tube.
Specific details for manufacture of modern day casings from viscose into regenerated cellulose are shown in U.S. Pat. Nos. 2,999,756 and 2,999,757 to Shiner; U.S. Pat. No. 3,835,113 to Burke, U.S. Pat. No. 4,590,107 to Bridgeford; U.S. Pat. No. 4,778,639 to Jon; and U.S. Pat. No. 5,358,765 to Markulin. These references describe extruding viscose (sodium cellulose xanthate, sodium hydroxide, water) through an annular die into a coagulating and regenerating bath to produce a regenerated cellulosic tubular casing. An alternative method for forming cellulosic casings known as the solvent spinning process using N-Methylmorpholine N-oxide solutions of cellulose is described in U.S. Pat. No. 5,277,857 and U.S. Pat. No. 5,451,364.
Artificial sausage casings are shirred according to conventional methods wherein long tubular lengths, often called "strands," are compacted to provide shorter, coherent tubes, often called "shirred sticks" or "sticks." The coherency of the stick is important in order that it remain straight and rigid. This is difficult to achieve, considering the shirring operation includes moisturizing and oil addition. Conventional shirring methods are illustrated by patents such as U.S. Pat. No. 2,001,461; U.S. Pat. No. 2,010,626; U.S. Pat. No. 2,583,654; U.S. Pat. No. 2,722,714; U.S. Pat. No. 2,983,949; U.S. Pat. No. 2,984,574; U.S. Pat. No. 3,097,393; U.S. Pat. No. 3,110,058; U.S. Pat. No. 3,397,069; U.S. Pat. No. 3,454,982; and U.S. Pat. No. 3,898,348. Chiu, U.S. Pat. No. 3,898,348 describes a coherency test of applying a beam bending moment to the shirred stick, with 1.0 inch-lbs bending moment being the minimum acceptable standard, and 2.5 inch-lbs being desired. Accordingly, it is well known in the art that coherency of the shirred stick is essential for utility.
Small diameter shirred food casings must be packaged for distribution and sale, and this packaging is critical to the performance of the commercial product because the casing has a thickness of 20 to 40 microns and can be easily damaged. Accordingly, the shirred sticks must be rigidly supported to prevent dimension deformation, survive the rigors of transportation, and yet be easily dispensed without much waste packaging at the final use. The shirred casing product is then filled with meat paste using high speed filling machines. The stuffing operation will handle sticks typically from 265 mm length to 546 mm length, containing casing typically ranging from 16.5 meters up to and in excess of 69 meters. Thus, one shirred stick could provide in excess of 500 frankfurters. Any defects in the stick are therefore costly to the meat processor.
As one aspect of the shirring process, it is known that administration of a shirring solution to the casing interior provides various advantages during shirring and thereafter during removal of the casing from the cooked sausage by peeling. Administration of the internal shirring solution moisturizes the casing, allowing it to achieve final humidity and to avoid breakage and further allows for the addition of peeling and release agents to the interior of the casing. Moreover, the casing shrinks slightly (about 1% to 3%) upon being wetted by solution with this shrinkage greatly reinforcing the internested cones formed during shirring and providing improved coherency to the shirred sticks.
One preferred material for shirring of cellulose food casings is white food grade mineral oil. U.S. Pat. No. 2,983,949 to Matecki outlines the use of White U.S. Mineral Oil of Saybolt viscosity 76.degree. to 80.degree. in the internal inflation air stream of the shirring machine. Other lubricants including cotton seed oil, soya oil, glycerine are also known for coating the inside surface of the casings. Oil is generally applied internally at a rate of from 5 to 25 mg per 100 square inches. Lubricating oil is also shown by Matecki to be applied to the external casing, both to lubricate the shirring rolls to prevent heat build up and to lubricate the casing to prevent damage during shirring and later stuffing with meat emulsion. In U.S. Pat. No. 3,097,393, Matecki specifies the use of White Mineral Oil, Saybolt viscosity 76.degree. to 80.degree. for external coating of casings with coverage onto the casing of between 0.002 grams to 0.013 grams per 6 inch casing length. Oil is thus generally applied externally at a rate of from about 20 to about 100 mg per 100 square inches.
Marbach, U.S. Pat. No. 3,110,058 shows a typical system for spraying internal liquids. Marbach also shows in U.S. Pat. No. 3,158,896 a means of using a commercial force-fed lubricator to apply this mineral oil. Arnold, U.S. Pat. No. 3,222,192 shows using water as the external lubricant for the shirring rolls, as well as for a means of increasing shirred stick moisture to the desired ratio of 17% to 18% by total weight of all components. Arnold also describes adding the moisture internally to the stick inside wall during shirring as an alternate method and adding surface active agents to increase wettability. Prior to this, casings were humidified externally in the packaged state as shown by Patents U.S. Pat. No. 2,181,329; U.S. Pat. No. 2,794,544; U.S. Pat. No. 3,028,952 and U.S. Pat. No. 3,250,629.
Clement in U.S. Pat. No. 3,266,911 shows the external oiling system describing mineral oil as the external lubricant. Bridgeford shows in U.S. Pat. No. 3,451,827 a mandrel designed to internally spray coatings onto the casing inner walls during shirring using compressed air as the propellant and exhausting the excess air. Bridgeford also discloses the use of external lubricating oil. Suitable lubricating oils include but are not limited to mineral oil, vegetable oils and glycerols with various additives including lecithin and carboxymethylcellulose.
Martinek in U.S. Pat. No. 3,456,286 teaches a means for using Bridgeford's technology to tightly compact casing. Martinek, U.S. Pat. No. 3,462,794 also discloses a fluid applicator to apply external shirr moisture to the casing, coincident with internal addition. Michl in U.S. Pat. No. 3,594,856 also added external moisturizing to the casing, post-shirring. Voo, U.S. Pat. No. 3,616,489 discloses a system to spray the shirred stick internal bore after shirring. Rose, U.S. Pat. Nos. 3,818,947 and 3,834,920 discloses using a mineral oil coating inside (N.F. No. 9) along with a surfactant Myvacet 9-45 (acetylated glycerol monooleate) to more uniformly coat the mineral oil.
Chiu, U.S. Pat. No. 3,898,348 shows that the shirring solution can serve as a peeling agent, moisturizing agent and shirrability enhancer. Chiu teaches the use of shirring solutions comprising mixtures of water soluble cellulose ethers such as carboxy-methyl cellulose (CMC), mineral oil, surfactants (preferably polysorbate surfactants available as Tween.RTM. (ICI Chemicals)), and water, with polyols such as glycerine, sorbitol, propylene glycol and triethylene glycol being used as humectants to retard the penetration of the spray into the casing. Shirr solutions were taught to preferably be applied at 25.degree. C. temperature (i.e., ambient room temperature) and were said to be characterized by viscosities of 500 cps with a maximum of 1500 cps. It is theorized that if the shirring solution penetrates slowly, the casing does not experience shrinkage while it is on the shirring machine. As a result, the tendency of the casings to seize the mandrel is reduced and the products can be manually transferred and manipulated on the shirring machine. Chin shows that reducing the humectant (i.e. propylene glycol) in the shirr solution allows faster water penetration increasing the rate of casing shrinkage and thus affecting the ability to slide the casing on the mandrel. However, if too much humectant is used, dimensional change can occur for several days after shirring in a relatively uncontrolled state resulting in excessive and undesirable dimensional change. Chiu, U.S. Pat. No. 3,981,046 further taught the use of propylene glycol as a humectant where the moisture of the final casing was produced in excess of 17% by using a humectant during shirring to reduce the rate of water imbibition by the casing.
Developments in the art since Chiu have resulted in a reduction of the quantity of propylene glycol added during shirring. While a 60% propylene glycol concentration in the shirr spray was typical at the time of Chiu, propylene glycol concentrations have more recently dropped to about 10% while other methodologies have been introduced to allow the sticks to be transferred easily without the retardation of water. It is known in the art that when levels of propylene glycol are reduced, it becomes more difficult to remove the shirred stick from the mandrel after compression due to the shrinkage exerted by the stick onto the mandrel. The casing can be damaged and the mandrel itself can bend and be damaged. Forces of several hundred pounds are not uncommon for stripping the shirred stick. Accordingly, it is now common to use very smooth surfaces such as those coated with Teflon.RTM. non-stick coatings to allow easier removal typically as disclosed in U.S. Pat. No. 3,097,393. Nevertheless, smooth coatings are difficult to use and still cause flattening of pleats and result in the radial reduction of the bore of the shirred stick. It is also known to taper the mandrel diameter towards the end of travel to alleviate the pressure. This can result in a smaller than desired stick bore (inner diameter) and often causes non-uniformity of stick inner and outer diameters.
Much effort in the art has been addressed toward alternative methods for improving the coherency of shirred casings. Winokur, U.S. Pat. Nos. 3,695,901 and 3,909,882 disclose methods for providing higher coherency by indenting the stick outer diameter with grooves. Rasbach, U.S. Pat. No. 3,798,301 discloses passing the shirred stick through a heated annular orifice to increase stick coherency.
Wilson, U.S. Pat. No. 4,062,980 discloses using sorbitan trioleate and glycerol monooleate as surfactants of the humidification fluid. Bridgeford in U.S. Pat. Nos. 4,062,981 and U.S. Pat. No. 4,137,947 describe use of sorbitan trioleate as a lubricating surfactant for the shirring spray, providing wettability and anti-jamming properties, yet achieving 14% to 20% shirred stick moisture. The method also reduces post-doffing stick expansion.
Hammer, U.S. Pat. No. 4,248,900 describes applying the release agents prior to shirring, winding the casing up, and then later shirring. Bridgeford in U.S. Pat. No. 4,489,114 combines arabinogalactans with cellulose ether to improve peelability by improving resistance to gluing of the pleats due to the cellulose ethers on the interior side. Hutschenreuter in U.S. Pat. No. 4,528,225 describes peeling systems of oils, cellulose ethers and chemical starches.
Hammer, U.S. Pat. No. 4,543,282 describes application of the shirring spray at ambient temperature, that is between 15.degree. C. and 30.degree. C., using various combinations of waxes, silicone oils and cellulose ethers. Alternate mixtures by Hammer are shown in U.S. Pat. No. 4,563,376. Higgins in U.S. Pat. No. 4,596,727 provides shirring solutions using Mazol 80 MG as a surfactant but maintaining propylene glycol at 22.5% to 49.00% in solution with final shirred stick moisture contents of 17% to 19.3%.
Stall in U.S. Pat. No. 4,818,551 recognized the dimensional change of shirred sticks and provided for this by maintaining the shirred casing on a dowel for 72 hours after shirring to allow full penetration of the shirr spray without loss of dimensional integrity of the shirred stick.
Bridgeford in U. S. Pat. No. 4,844,129 uses polydextrose additives for prevention of pleat lock. Apfeld in U.S. Pat. No. 5,230,933 uses a water soluble cellulose ether, dextrin, as a coherency enhancer and, optionally, lecithin as a peeling acid, optionally with a surfactant. Lecithin has been used by others, such as Japanese Patent 1632287/1982 to Suguro and Spanish Patent 549,161/4 to Michelena.
Of interest to the present invention is the disclosure of co-owned and copending U.S. application Ser. No. 08/703,796 filed Aug. 27, 1996 relating to methods and compositions for carrying out cold temperature shirring methods, the disclosure of which is hereby incorporated by reference.
In the manufacture of sausage such as hot dogs via the emulsion process, the meat emulsion has a pronounced tendency to adhere to the cellulosic casings, making it difficult to achieve rapid removal of the casings from the final finished meat product. Peeling of casings is typically carried out by automatic mechanical peelers. Nevertheless, in order to assist such peeling processes a steam shower may be used to loosen the casing from the sausage product. While the methods described previously improve the peelability of the skin by use of various shirring coatings including oils and carboxymethyl cellulose solutions, there nevertheless remains a desire in the art for means by which the peelability of sausage casings may be improved.